Studies of induction of infectious virus from SV40 virus transformed hamster kidney cells include investigations of the mechanism of excision of the viral DNA from the host cell genome, and the kinetics of both DNA and late mRNA synthesis subsequent to induction. The relationship between breaks in the host cell DNA subsequent to various forms of induction by radiation and rescue of infectious virus are being investigated. Studies on the cell surface are concerned with the role of the sulfated acid mucopolysaccharides and various cellular proteases in the maintenance of the transformed cell phenotype. Our experiments indicate that cell proteases are produced throughout the cycle in transformed cells but only during growth in normal cells, i.e. contact inhibited, normal cells do not elaborate cell proteases. These experiments suggest that cellular proteases are associated with growth and, possibly, the changes in the cell phenotype which occur during mitosis. Experiments with antiproteases indicate that the large molecular weight glycoprotein (250,000 M.Wt.) which is absent from transformed cells may reappear subsequent to treatment with EACA. This suggests that proteolysis of the cell surface may be responsible for the loss of this protein in transformed as well as growing, normal cells. Studies on virus transformed programmed spleen cells indicate that monospecific antibody is produced by these cells. Experiments utilizing cell surface mitogens and antigens reveal that increased amounts of this antibody are produced subsequent to such treatment. The mechanism of increased antibody production is being investigated.